At Supercomputing 98 at Orlando, Florida, November 1998

don't miss

Superball .... a.k.a. voodoo

by John Estabrook, Ulises Cervantes-Pimentel, George Francis

Voodoo is a real-time interactive computer animation for
three players to inhabit the same virtual environment, two on
the DuoDesk and the third in the CAVE. We use Dave Pape's "zaphod"
version of the CAVE library for the 2 head tracked, 2 hand tracked
Immersadesk to be installed in Orlando, and the standard CAVE
library in the CAVE in Urbana. The two SGI Onyx's (shared memory
parallel super-computers) driving the virtual environments talk
over standard UDP protocol by means of Caterpillar's
"Virtual Prototyping File Format" (VPS) libraries,
courtesy Volodymyr Krindratenko and Lance Arsenault.

Since we expect serious latency problems, including total dropout of
communication, the two instances, voodoo.cave and voodoo.duo, operate
independently. Trajectories of some movables (the gravitational lens,
the paint-balls launched by the player's avatars, etc) are locally
anticipated but periodically corrected as data arrives from the distant
partners. The three avatars visible in the scene, however, are kept
current by VPS.

The immovable scene consists of Stuart Levy's stars at "infinity", three
walls of the CAVE (the backwall features highbrow texturemapped paintings,
the side wall remains a wireframe, the floor is paved with $100 bills),
and a barber pole. The movables consist of the invisible "gravitional
lens", the avatars and their paint-balls. We use Birgit Bluemer and
John Estabrook's generalization of the classic Einstein approximation
to his relativistic field equations.
The lens distorts the background and also produces a
second, socalled "inner image", as specified by Einstein's relativistic optics.
The lens drifts about an invisible cube, bouncing off the walls.

Each player can experience Einstein's distortion, or, she can observe how
this illusion is confected by cycling through the "ecstasy modes". In ecstasy
(standing outside one-self) a player sees the per-vertex deformation of the
scenery induced by the instantaneous location of the lens relative to
another observer .

The avatar mimics its player's head and hand, and was designed by artist
Kris Moskwa. Hand gestures control the motion of the player in the scene.
The player can also launch a paint-ball, which drifts
(more-or-less predictably)
towards the intended movable target (another avatar or the presumptive
location of the lens when they collide). If contact is made a signal is
displayed (someday we'll use vss to make appropriate sounds) and the paint-ball
returns to the avatar's wrist, marking the pivot point of the hand.

The actual performance of this piece is excrutiatingly sensitive to the
performance of the multiprocessor onyxes and especially to the network.
We have made every effort to finagle the action so that every malfunction
can be blamed on others.